Reverse Engineering: Printed Circuit Boards Rev II

Transcription

1 Reverse Engineering: Printed Circuit Boards Rev II DR. T A R E K A. T U T U N J I R E V E R S E E N G I N E E R I N G P H I L A D E L P H I A U N I V E R S I T Y, J O R D A N

2 References PCB Reverse Engineering by John Armistead A Rapid Prototyping Methodology for Reverse Engineering of Legacy Electronic Systems by Deno, Landis, Hulina, and Balasubramanian Deconstructing the circuit board sandwich by Joe Grand, Grand Idea Studio

3 The Need for PCB RE Replace an obsolete PCB that is no longer available from the original manufacturer. Old PCBs are sometimes difficult to support: Increasing costs of spare parts Non-existent procurement sources. The technical documentation needed to re-manufacture replacement parts is often insufficient or non-existent. Missing manufacturing files such a Gerber files are often sited as the main reason.

4 PCB Re-Engineering Re-engineering a PCB assembly can provide an improved or added performance to an old process. New and improved materials and techniques may be utilized to improve operations, maintenance and support. Reverse engineer your PCB first as a base set of data and then modify that base to obtain a more modern PCB that is both less expensive to build and less expensive to service.

5 Needed Documentation PCB layer count and physical board dimensions. Padstack definitions and coordinate locations of the pads on the board. Component definitions and functional component specifications. Netlist information defining inter-component connections.

6 PCB RE Steps 1. Prescreen 2. Observe 3. Disassemble and identify components 4. Identify connections and capture schematic 5. Generate Gerber files for the board

7 PRESCREEN AND OBSERVE

8 1. Prescreen The selection of potential candidates for the reverse engineering cycle depends on economics, technical complexity and the amount of existing data. Components that have high usage and high per-unit cost but relatively low technical complexity are good candidates for the reverse engineering process. Obtain at least two samples of the board

9 2. Observe Evaluate existing data Drawings and technical manuals that provide information about the PCB assembly are collected. Usage and maintenance data are also obtained along with performance specifications. The physical unit is visually inspected and discrepancies between the available data and the actual PCB are noted. Identify some components and obtain specifications for each.

10 2. Observe Formulate a management plan including minimum requirements of an acceptable Technical Data Package (TDP). The objective of this stage is to complete the TDP, which will be sufficient for fabrication and procurement of the PCB assembly.

11 DISASSEMBLE AND IDENTIFY COMPONENTS

12 3. Disassemble and Identify Components The PCB is disassembled. A list characterizing each piece and the order of disassembly is maintained. Component availability is verified and exceptions are researched for substitutes

13 3. Disassemble and Identify Components This process will make one sample board unusable again. The second board is used as reference. The identification of all components is required for the bill of materials (BOM). Unpopulated PCB Populated PCB

14 3. Disassemble and Identify Components Most vendors and part numbers printed on the components. Small devices use an abbreviated code Abbreviation details available in manufacturer data sheets Educated guesses will help narrow down part

15 3. Disassemble and Identify Components Basic identification tips: Look for manufacturer's logo Look for alphanumeric string on part Find data sheets Data sheets contain extremely useful technical component information: Product overview Pinout and pin function Electrical parameters and functional limits Package drawings

16 Data Sheet Example

17 3. Disassemble and Identify Components Sometimes, sensitive targeted components are made intentionally difficult to access Some vendors remove identifiers and markings from ICs May still be able to identify parts without the markings by probing or following important looking traces/signals

18 3. Disassemble and Identify Components Websites that help to find datasheets

19 3. Disassemble and Identify Components Look for Probe/Testing points

20 3. Disassemble and Identify Components

21 3. Disassemble and Identify Components

22 IDENTIFY CONNECTIONS AND CAPTURE SCHEMATICS

23 4. Identify Connections and Capture Schematic Use the unpopulated PCB to identify the circuit schematic. Identify all of the electrical connections between components on the board Node list, sometimes called a net list This process requires an experienced electrical engineer to be able to render the emerging node list into a readable schematic. Build the schematic Capture the schematic in software including building component images for all components that are not in a parts library.

24 Separate the PCB layers Separate layers to identify each layer and construct a complete circuit layout If components are also known, a full electrical design can be reversed Example: 4-layer PCB Ref. Grand Ideas Studies

25 Solder Mask Removal Sandpaper Fiberglass Scratching Chemicals Laser Ref. Grand Ideas Studies

26 Delayering CNC Milling Dremel Tool Ref. Grand Ideas Studies

27 X-Ray Imaging Ref. Grand Ideas Studies

28 GENERATE GERBER FILES

29 5. Generate Gerber Files The Gerber format is a file format used by PCB industry software to describe the images of a printed circuit board (copper layers, solder mask, legend, etc.) as well as the drilling and milling data. The Gerber format is the de-facto industry standard for printed circuit board image transfer

30 Example Gerber layers, showing the top overlay (legend), top solder resist (protective film), top layer copper traces, and bottom layer copper traces of a printed circuit board %AMMACRO19* 21,1,.0512,.0512,0.0,0.0,45.*% %ADD19MACRO19*% %LPD*% G75* G54D10* X176250Y117500D03* Y130000D03* Y163750D03*...

31 Re-engineering: Design Verification Prior to prototype fabrication and testing, the technical data package is reviewed for accuracy and completeness. Prototypes are built and tested. Deficiencies in the results from prototype testing follow traditional debugging procedures and lead to final modifications and improvements in the TDP

32 Patent / Copyright Issues If a board has a copyright mark, then you should not reverse engineer the traces verbatim. Rerouting the board using any one of the auto router software packages will generally render a board that is unlike the existing board although still electrically and schematically identical. The majority of the patented boards are patented for onboard firmware or highly specialized digital circuits. Unless you have very deep pockets, this is one PCB reverse engineering area that it is advisable to stay away from altogether. Of course, if your company owns the patent then there is no problem.

33 PCB RE Results Complete schematic diagrams. Includes any on board, point to point, wiring diagrams. Complete bill of materials including individual data sheets on each component. Complete Gerber files for the production of the PCB. A prototype PCB assembled with components for testing and evaluation

34 Conclusions Reverse engineering PCB's is a necessary process to obtain lost manufacturing files. Sometimes, reverse engineering combined with reengineering can revitalize old circuits to save time and money. Reverse engineering, redesign or re-engineering your PCB assemblies can be done quickly and economically. Original drawings can be provided with a pre-production prototype for testing and evaluation.